Process for cracking paraffins to olefins

ABSTRACT

This invention is a process for the catalytic cracking of parafins to produce olefins in high yield while minimizing production of aromatics. The catalyst used is a zeolite in combination with an alkali(ne earth) metal compound wherein the sum of the amount of the alkali(ne earth) metal in the compound plus any metal cation exchanged into the zeolite is in excess of that required to provide a fully metal cation-exchanged zeolite.

This is a continuation of application Ser. No. 07/576,247, filed Aug.31, 1990, now abandoned.

FIELD OF THE INVENTION

This invention relates to a process for the catalytic cracking ofparaffins to olefins, particularly straight chain paraffins to straightchain olefins.

BACKGROUND OF THE INVENTION

Zeolites are known as useful for the catalytic cracking of hydrocarbonfeedstocks, particularly feedstocks containing feedstocks. The problemwith the use of conventional zeolites as catalysts for the cracking ofparaffinic feedstocks is that they produce a variety of products:olefins, both branched and straight chain, aromatics, paraffins andother products resulting from dealkylation, aromatic side-chainscission, isomerization, condensation and disproportionation reactions.A catalytic cracking process that would produce only olefins insubstantial quantities would be of commercial significance, since theolefins can be used as feedstocks to produce higher valued end products.

Olefins serve as feedstocks for the chemical industry. They can beconverted to corresponding alcohols or aldehydes. Higher molecularweight alcohols can further be ethoxylated with ethylene or propyleneoxide in the presence of a catalyst to form conventional detergentswhile lower molecular weight alcohols can be esterified with aromaticacids to form plasticizers.

SUMMARY OF THE INVENTION

This invention relates to a process for the catalytic cracking ofstraight chain paraffins to produce straight chain olefins whichcomprises contacting said paraffins with a catalyst comprising a zeoliteand an alkali(ne-earth) metal compound wherein the sum of the amount ofthe alkali(in-earth) metal in the compound plus any metal cationexchanged into the zeolite is in excess of that required to provide afully metal cation-exchanged zeolite. The product of this processcontains only small amounts of aromatics and branched olefins.

DETAILED DESCRIPTION OF THE INVENTION

The term "alkali(ne-earth) metal" as used hereinafter refers to a metalselected from the group consisting of alkali metal, alkaline earth metaland mixtures thereof, that is, it refers to alkali metal and/or alkalineearth metal and includes one or more alkali metals, one or more alkalineearth metals and two or more of a mixture of alkali metal(s) andalkaline earth metal(s).

Catalytic Cracking Process

This instant invention provides a catalytic cracking process forconverting normal paraffins, that is straight chain aliphatichydrocarbons to normal, that is straight chain olefins. Useful paraffinsfor the instant process range from C₄ to C₃₅ and above. These paraffinsmay be liquid at room temperature such as the C₄ -C₂₀ group or solid atroom temperature such as the C₂₁ -C₃₅ and above group, or mixtures ofboth groups. The catalytic cracking is carried out in a gas and/orliquid phase at catalytic cracking conditions.

Any suitable reactor can be used for the catalytic cracking process ofthis invention. For example, a fixed bed of catalyst particles can beused, with paraffin feedstock passing through the catalyst bed atcatalytic cracking conditions. Generally in commercial operations it isanticipated that a fluidized-bed catalytic cracking (FCC) reactor(preferably containing one or more risers) or a moving-bed catalyticcracking reactor (e.g., a Thermofor catalytic cracker) is employed,preferably a FCC riser cracking unit. Examples of such FCC crackingunits are described in U.S. Pat. Nos. 4,377,470 and 4,424,116. Generallya catalyst regeneration unit (for removal of coke) is combined with theFCC cracking as is shown in the above-cited patents.

Specific operating conditions of the cracking operation depend greatlyon the type of feed, the type and dimensions of the cracking reactor andthe feed rate. Examples of operating conditions are described in theabove-cited patents and in many other publications. In an FCC operation,generally the weight ratio of catalyst to feed ranges from about 2:1 toabout 10:1. the contact time between oil feed and catalyst is in therange of about 0.2 to about 2 seconds, and the cracking temperature isin the range of from about 350° C. to about 650° C. Generally steam isadded with the oil feed to the FCC reactor so as to aid in thedispersion of the oil as droplets. Generally the weight ratio of steamto oil feed is in the range of from about 0.05:1 to about 0.5:1.Pressures will typically range to about atmospheric to about fiveatmospheres. For fixed bed reactors temperatures and pressures aresimilar to those of an FCC reactor with liquid hourly space velocitiestypically ranging from about 0.1 to 10 hours⁻¹. The product of theinstant process can be used as such as feedstocks for processesrequiring olefins or it can be further purified before such use byconventional means such as distillation or fractional crystallization.

The Cracking Catalyst

The catalysts that are utilized in the process are described inco-pending U.S. patent applications Ser. No. 354,586, filed Jun. 22,1989 and Ser. No. 387,265, filed Jul. 31, 1989, incorporated byreference herein.

Essentially any crystalline zeolitic aluminosilicate can be employed toprepare the catalysts utilized in the instant process. The zeolites caninclude both synthetic and naturally occurring zeolites. Illustrative ofthe synthetic zeolites are Zeolite X, U.S. Pat. Nos. 2,882,244; ZeoliteY, 3,130,007; Zeolite A, 2,882,243; Zeolite L, Bel. 575,117; Zeolite D.Can. 611,981; Zeolite R, 3,030,181; Zeolite S, 3,054,657; Zeolite T,2,950,952; Zeolite Z, Can. 614,995; Zeolite E, Can. 636,931; Zeolite F,2,995,358; Zeolite O, 3,140,252; Zeolite W, 3,008,803; Zeolite Q,2,991,151; Zeolite M, 2,995,423; Zeolite H, 3,010,789; Zeolite J,3,001,869; Zeolite W, 3,012,853; Zeolite KG, 3,056,654; Zeolite SL,Dutch 6,710,729; Zeolite Omega, Can. 817,915; Zeolite ZK-5, 3,247,195;Zeolite Beta, 3,308,069; EU-1, 4,537,754; Zeolite ZK-4, 3,314,752;Zeolite ZSM-5, 3,702,886; Zeolite ZSM-11, 3,709,979; Zeolite ZSM-12,3,832,449; Zeolite ZSM-20; 3,972,983; Zeolite ZSM-35, 4,016,245; ZeoliteZSM-50, 4,640,829; synthetic mordenite; the so-called ultrastablezeolites of U.S. Pat. Nos. 3,293,192 and 3,449,070; and the referencescited therein, incorporated herein by reference. Other syntheticzeolites are described in the book "Zeolite Molecular Sieves-Structure,Chemistry and Use," by Donald W. Breck. 1974, John Wiley & Sons,incorporated by reference herein. Illustrative of the naturallyoccurring crystalline zeolites are analcime. bikitaite, edingtonite,epistilbite, levynite, dachiardite, erionite, faujasite, analcite,paulingite, noselite, ferrierite, heulandite, scolecite, stilbite,clinoptilolite, harmotone, phillipsite, brewsterite, flakite, datolite,chabazite, gmelinite, cancrinite, leucite, lazurite, scolecite,mesolite, ptilolite, mordenite, nepheline, natrolite, scapolite,thomsonite, gismondine, garronite, gonnardite, heulandite, laumontite,levynite, offretite, yugawaralite. Descriptions of certain naturallyoccurring zeolites are found in the aforementioned book by Breck, in thebook "Molecular Sieves-Principles of Synthesis and Identification", R.Szostak, Van Nostrand Reinhold, New York, 1989, both incorporated byreference herein, and in other known references. These zeolites may bein the hydrogen form or may be partially or fully exchanged withammonium or metal ions.

As used herein, the term "compound" as applied to alkali(ne-earth) metalrefers to the combination of alkali(ne-earth) metal with one or moreelements by chemical and/or physical and/or surface bonding, such asionic and/or covalent and/or coordinate and/or van der Waals bonding,but specifically excludes that bonding involved between analkali(ne-earth) metal and a zeolite when such alkali(ne-earth) metal islocated in a cation exchange site of the zeolite. The term "ionic" or"ion" refers to an electrically charged moiety; "cationic" or "cation"being positive and "anionic" or "anion" being negative. The term"oxyanionic" or "oxyanion" refers to a negatively charged moietycontaining at least one oxygen atom in combination with another element.An oxyanion is thus an oxygen-containing anion. It is understood thations do not exist in vacuo, but are found in combination withcharge-balancing counter ions. The term "oxidic" refers to a charged orneutral species wherein an element such as an alkali(ne-earth) metal isbound to oxygen and possibly one or more different elements by surfaceand/or chemical bonding. Thus, an oxidic compound is anoxygen-containing compound, which also may be a mixed, double, orcomplex surface oxide. Illustrative oxidic compounds include, by way ofnon-limiting example, oxides (containing only oxygen as the secondelement), hydroxides, nitrates, sulfates, carboxylates, carbonates,bicarbonates, oxyhalides, etc, as well as surface species wherein thealkali(ne-earth) metal is bound directly or indirectly to an oxygeneither in the substrate or the surface. "Surface" as applied to zeolitesand the instant catalysts refers to external surface as well as theinternal pore surface, the internal surface being both the surface ofthe macro pores resulting from the agglomeration of individual particlesor crystallites as well as the surface of the mesopores and microporesand supercages that result from the intrinsic zeolite crystal structure.The term "salt" as used herein is meant to encompass a single salt aswell as mixtures of two or more salts. The term "alkali metal" is usedherein as a descriptor of the elements of Group IA of the Periodic Tableof the Elements (Li, Na, K, Rb. Cs, Fr). The term "alkaline earth metal"is used herein as a descriptor of the elements of Group IIA of thePeriodic Table of the Elements (Be, Mg, Ca, Sr. Ba, Ra) Alkali(ne-earth)metal herein does not refer to the element in the metallic or zerovalent state, but rather is a shorthand use for the element in thepositive valent state, that is, it will be understood to be combined asa salt, compound, complex, etc. The term "basic" refers to having thecharacteristic of a base; e.g., when placed in a solution, a basicmaterial will have a pH consistent with a base rather than an acid and,if a catalyst, will catalyze chemical reactions that are catalyzed bybases.

The alkali(ne-earth) metal salts that are suitable for preparing thecatalysts utilized in the instant process are any salts that can bedissolved in a suitable impregnating solution or which can be melted toform their own impregnating solution or which can be sublimed andcondensed on the zeolite. Illustrative but non-limiting examples ofsuitable salts are alkali(ne-earth) metal bicarbonates, carbonates,chlorates, perchlorates, cyanides, hydroxides, iodates, nitrates,nitrites, sulfates, hydrogen sulfates, sulfites, dithionates,thiosulfates, alkoxides, carboxylates, sulfonates, iodates, halides andthe like. Of the alkali(ne-earth) salts that can be utilized in theinstant invention, the hydroxide salts, particularly of alkali metals,are less preferred for providing the major portion of the alkali (neearth) compound since these strongly basic salts in high concentrationscan contribute to a degradation of the crystallinity of the zeolite.Salts which can be solubilized in a suitable solution are preferred.Preferred salts are those which have an oxygen-containing anion oroxyanion or which can be precipitated in situ with oxyanion. Usefulsalts are those which decompose at least in part upon calcination in thepresence of the zeolite to provide an alkali(ne-earth)metal-oxygen-containing moiety (e.g., Na--O--,Ca--O--, etc.), that is,produce an oxidic compound. When the alkali(ne-earth) metal salt isassociated with an anion which does not contain oxygen it is necessarythat the salt be precipitated in situ with a suitable oxyanion, oralternatively, after impregnation, the subsequent calcination is carriedout in an oxygen-containing atmosphere to cause the salt to react withthe oxygen to provide the alkali(ne-earth) metal-oxygen-containingmoiety, that is, produce an alkali(ne-earth) metal oxidic compound.Decomposition can be indicated by the evolution of gases such as carbonoxides, nitrogen oxides, sulfur oxides etc. Decomposition will also beindicated by disappearance at least in part of the particular anionicform associated with the alkali(ne-earth) metal in the impregnationliquid. For example, when carboxylates and alkoxides are calcined thecarboxylate and alkoxide moiety associated with the alkali(ne-earth)metal will decompose giving off carbon oxides and/or water and/orhydrocarbons, thereby disappearing at least in part. Particularlypreferred salts to be used in an impregnating solution are (alkali)carbonates nitrates and carboxylates. Mixtures of alkali(ne-earth) metalsalts, that is, two or more salts with differing anions, differingcations or differing anions and cations can be utilized to prepare theimpregnated zeolite.

One method that can be used to prepare the catalysts utilized in theinstant process involves the use of molten alkali(ne-earth) metal saltto impregnate the zeolite. In this method a suitable salt, that is, onemelting below about 850° C., is melted and the zeolite is added to themolten salt or the molten salt is added to the zeolite causing themolten salt to impregnate the pores of the zeolite. A very suitableimpregnation technique is to utilize that amount of molten salt that isequal to or less than that amount of molten salt that will just fill thepores of the zeolite. Alternatively, zeolite particles can be immersedin a molten salt bath to cause impregnation of the molten salt into thezeolite followed by separation of the excess molten salt from thezeolite, say by filtration, centrifugation or washing. Alternatively,zeolite particles can be coated with finely divided particles of asuitable alkali(ne-earth) metal salt and heated to above the meltingpoint of the salt, causing the molten salt to impregnate the pores ofthe zeolite. Many other methods, such as fluid bed impregnation orspraying molten salt or solid salt onto zeolite in a rotating kiln willbe obvious to one skilled in the art. After impregnation, theimpregnated zeolite is calcined to produce the catalyst utilized in theinstant process. The calcining temperature may be the same or lower thanthe impregnating temperature but frequently it is higher. Drying is notrequired when the molten salt technique is utilized, but may be utilizedto remove residual water remaining in the zeolite. The impregnation andcalcination can be carried out in one continuous step or sequence. Thealkali(ne-earth) metal nitrates and carboxylates are particularlysuitable for use in the molten impregnation method.

Another method is to use a sublimable alkali(ne-earth) metal salt. Inthis method a suitable salt is sublimed at above its sublimationtemperature to produce a vaporous salt and the resulting vapor iscontacted with the zeolite maintained at a temperature near or below thesublimation temperature of the salt thereby causing the vapor tocondense upon and within the pores of the zeolite thereby impregnatingit. Calcination follows to prepare the catalysts utilized in the instantprocess. Drying before calcination is not required in this case, but maybe utilized to remove residual water in the zeolite. The impregnationand calcination can be carried out in one continuous step or sequence.

Most conveniently and preferably, solutions of alkali(ne-earth) metalsalts are used to impregnate the zeolites. The solvents utilized todissolve the salts may be organic or inorganic. The only requirement isthat the desired salt be soluble in the particular solvent. Hydroxylicsolvents are preferred. Water is a particularly preferred solvent. Thelower alkanols are also particularly suitable for use with salts havingstrong basicity in water in order to minimize base-zeolite structureinteractions during the impregnation process. Organic solvents areparticularly useful as solvents for alkali(ne-earth) metal salts whichhave organic ionic components such as carboxylate, sulfonate, alkoxide,etc. Organic solvents are also useful for inorganic alkali(ne-earth)metal salts. Alkal(ine earth) metal salts having a low solubility in anorganic solvent can be used with that solvent to provide small, but wellcontrolled amounts of alkali(ne-earth) metal to the zeolite whileminimizing solvent-base-zeolite structure interactions. Illustrative,but non-limiting examples of organic solvents include alcohols,including polyhydric alcohols, ethers, esters, ketones, amides.sulfoxides and chloro/fluorohydrocarbons such as the various freons.Specific illustrative examples include methanol, ethanol, glycol,dimethyl ether, methyl acetate, methylethyl ketone, dimethyl formamide("DMF"), dimethyl sulfoxide ("DMSO"), N-methyl pyrrolidone ("NMP"),hexamethylphosphoramide ("HMPA"), dichlorodifluoromethane, methylchloride, ethylene dichloride, ethylene carbonate, etc. Illustrative,but non-limiting examples of inorganic solvents include water, liquidammonia, liquid carbon dioxide, liquid sulfur dioxide, carbon disulfide,carbon tetrachloride, etc. Mixtures of solvents which are mutuallymiscible may be utilized.

When the catalyst comprises a zeolite-alkaline earth metal compound, apreferred variation on the impregnation technique comprises impregnatingthe zeolite with a soluble salt of an alkaline earth metal salt,followed by contact or reimpregnation with a precipitating agent, suchas a suitable solubilized anion, that will form a precipitate in situwith alkaline earth metal ion. For example, a zeolite is firstimpregnated with an aqueous solution of barium or calcium nitrate orchloride. Then the impregnated zeolite, without intermediate dryingand/or calcining is contacted with an aqueous solution of ammoniumsulfate or hydroxide, causing barium or calcium sulfate or hydroxide toprecipitate within the zeolite. This resultant material is then dried asnecessary and optionally calcined. Gaseous precipitating agents may alsobe utilized. For example, after a zeolite is first impregnated with anaqueous solution of alkaline earth metal nitrate, it is then contactedwith or without intermediate drying with gaseous ammonia ordimethylamine, resulting in the precipitation of or conversion to thealkaline earth metal hydroxide. Preferred precipitating agents are thosewhich produce an oxidic compound or a compound which is converted to anoxidic compound upon calcination.

Single or multiple impregnations may be used. When multipleimpregnations are used intermediate drying steps, optionally followed byprecipitation and/or calcination may be utilized. Generally any amountof impregnating liquid can be used in the impregnation process. Forexample, the zeolite can be dipped into a large excess (compared to thepore volume of the zeolite), removed and shaken of excess liquid.Alternatively, an amount of impregnating liquid considerably less thanthe pore volume can be sprayed onto an agitated bed of zeolite. Forpurposes of economy, control and other reasons, the volume ofimpregnating liquid will preferably range from about the pore volume toabout four or five times, preferably about twice the pore volume of thezeolite to be impregnated. Alternatively, a "dry" impregnation techniqueis utilized wherein just that amount of impregnating solution is usedwhich will just fill the pores of the zeolite. In another embodiment,baskets of zeolite material are dipped into a vat of impregnatingsolution, removed, dried and optionally calcined.

The concentration of alkali(ne-earth) metal salts in the impregnatingsolution is not critical and is selected, inter alia, on the basis ofthe zeolite used, the amount of ion exchange capacity present in thezeolite, the degree of basicity of the final product desired, theimpregnation solvent used and the type of impregnation utilized, thatis, multiple or single. Concentrations of alkali(ne-earth) metal salt(s)in the impregnating solution will typically range from about 0.01 molesper liter to the solubility limit of the salt(s). A suitable range isfrom about 0.01 to about 20 moles per liter, more preferably from about0.1 to about 10 moles per liter.

The amount of alkali(ne-earth) metal which is impregnated into thezeolite must be in excess of that which would provide a fully cation-ionexchanged zeolite. For example, if the starting zeolite were completelyin the hydrogen form and had an ion exchange capacity of 12% (basis Na₂O), then the equivalent amount of alkali(ne-earth) metal impregnated(basis Na₂ O) must exceed the 12%. If the starting zeolite were onewhich had already been 80% exchanged with a metal cation, the amount ofalkali(ne-earth) metal to be added by impregnation would be in excess ofthat amount required to exchange the remaining 20%. If the startingzeolite were fully metal cation exchanged, then any amount ofalkali(ne-earth) metal in the impregnating solution would suffice. It isto be understood that impregnation of a partially or fullycation-exchanged zeolite will most likely result in some counter ionexchange between the impregnating alkali(ne-earth) metal cation(s) andthe cations already present in the zeolite, but the resulting catalystwill still be within the scope of the instant invention in having anexcess of alkali(ne-earth) metal present over the amount exchanged intothe fully exchanged zeolite. When the amount of impregnating solutionthat is utilized is such that after impregnation no excess solution isremoved, then the amount of alkali(ne-earth) metal salt in theimpregnating solution will be the same as the amount impregnated intothe zeolite. When an amount of impregnating solution is used thatrequires that an excess amount of solution must be removed, for example,by filtration or centrifugation, from the impregnated zeolite afterimpregnation, then the amount of alkali(ne-earth) metal in theimpregnating solution will exceed the amount of alkali(ne-earth) metalimpregnated into the zeolite. In this latter case, the amount ofalkali(ne-earth) metal impregnated into the zeolite can be determined bya knowledge of concentration of alkali(ne-earth) metal in theimpregnating solution before the impregnation, the concentration ofalkali(ne-earth) metal in the excess solution removed from theimpregnated zeolite and the amount of solution remaining afterimpregnation (the excess). Alternatively, the impregnated zeolite can beanalyzed for alkali(ne-earth) metal content.

In general it is preferred to have a slight excess of alkali(ne-earth)metal present. When considering as a basis for calculation the zeolitehaving no cations exchanged therein, the preferred catalysts will havethe sum of the alkali(ne-earth) metal in the alkali(ne-earth) metalcompound and any metal cation exchanged into the zeolite being greaterthan 1, preferably greater than about 1.05, more preferably greater thanabout 1.1, even more preferably greater than about 1.15, even morepreferably greater than about 1.2, even more preferably greater thanabout 1.5, even more preferably greater than about greater than about 2times the amount required to provide a fully cation-exchanged zeolite(or times the exchange capacity). When considering the fullycation-exchanged zeolite as a basis for calculation, the amount ofalkali(ne-earth) metal in the alkali(ne-earth) metal compound is greaterthan zero, preferably greater than about 0.05, more preferably greaterthan about 0.1, even more preferably greater than about 0.15, even morepreferably greater than about 0.2, even more preferably greater thanabout 0.5, and even more preferably greater than about 1 times theamount of alkali(ne-earth) metal that would be required to provide afully metal cation-exchanged zeolite (or times the exchange capacity).

After impregnation utilizing an impregnating solution or a subsequentprecipitating solution, the impregnated zeolite is dried to remove thesolvent of the impregnating and/or precipitating solution. The dryingconditions are not critical to the instant invention. Drying may becarried out at atmospheric pressure, superatmospheric pressure or undervacuum. It also may be carried out by passing a dry (with regard to theimpregnating solvent) gas over a bed of the zeolite. Drying temperatureswill depend upon the solvent used. For those solvents that are liquid atlow temperatures, such as liquid carbon dioxide or liquid sulfurdioxide, the drying temperature can be relatively low, that is, belowroom temperature. For the more conventional solvents which are liquid ator above room temperature, higher temperatures will be used. For thesesolvents temperatures will typically range from about room temperatureto about 200° C. In most cases drying temperatures will be less thanabout 200° C., preferably less than 150° C. Drying times are dependentupon the drying temperature and pressure, typically from about oneminute to about twenty hours, although longer or shorter times can beutilized. Drying atmospheres and pressures are normally not critical.The drying atmosphere may be neutral, oxidizing, reducing or a vacuum.

After drying to remove an impregnating solvent or after impregnation bymeans of a molten or vaporous salt, the impregnated zeolite isoptionally calcined at elevated temperatures. Calcination conditionswill range from about 150° C. to about 850° C., preferably from about200° C. to about 750° C., and more preferably from about 200° C. toabout 600° C. Calcining times are dependent on the calcining conditionsselected and typically range from about one minute to about twentyhours, although longer or shorter times can be utilized. Calciningconditions and times are also adjusted according to the thermalstability. Calcination conditions should not be so extreme as to causeextreme loss of zeolite crystallinity. Calcining atmospheres may beneutral, oxidizing or reducing. When the impregnating salt has ananionic component which does not contain oxygen, an oxygen-containingcalcining atmosphere is preferably utilized. Neutral atmospheres such asprovided by nitrogen and oxidizing atmospheres such as provided by airare preferred.

When using an impregnation or an impregnating/precipitating solution,the drying and calcining steps may be combined into one integratedprocess step. In this combined step the impregnated zeolite is heatedthrough the lower temperatures at a rate slow enough that physicaldisruption of the zeolite does not occur due to rapid volatilization ofthe solvent from the impregnation. After the solvent has been removed,the zeolite is then heated to the desired calcining temperature,maintained for the desired calcining time and then cooled to roomtemperature. Calcining (and drying) can be carried out in situ duringthe operation of a catalytic process in a catalytic reactor.

The exact form of the alkali(ne-earth) metal after calcination is notknown. Without intending to limit the scope of the instant invention, itis believed that the alkali(ne-earth) metal(s) is present as one or morealkali(ne-earth) metal oxidic compounds. It is speculated that thealkali(ne-earth) metal compound(s) are probably in the form of a surfaceoxide or multiple surface oxides with the zeolite, in particular withthe aluminum and/or silicon and/or oxygen of the zeolite lattice,possibly in combination with species contained in or formed from theimpregnation solution or during the calcination process.

The calcination contributes to the production of a catalyst which isbasic and this basic nature is thought to derive from the particularnature of the alkali(ne-earth) metal compound present after calcination.However, those catalysts produced by precipitation with a basicprecipitating agent are within the scope of the instant invention, evenwithout calcination taking place. The basic nature of these materialscan be seen from the fact that instant catalysts when placed in asolvent produce effects that are basic rather than acidic in nature.This can been seen by the use of suitable chemical or electrochemicalindicators.

The basicity of the instant catalysts can be determined in various ways.For example, it can be determined by measuring the extent to whichvarious base-catalyzed reactions are carried out in the presence of ofthe instant catalysts. Another method is to place the instant catalystin a solvent and measure the resulting pH by use of chemical orelectrochemical indicators. A specific example would involve placing 20mg of catalyst in 2 g of water and using a pH meter or pH paper tomeasure the resulting pH. Another method is to use various indicators innon-aqueous solutions and compare the indicator response caused by theinstant catalysts with the indicator response caused by selectedreference samples. Suitable indicators are 4-nitroaniline or4-chloroaniline dissolved in dimethyl sulfoxide ("DMSO") or benzene (@0.1 g/cc). Examples of indicator responses with various referencesamples is shown in Table 1 below.

                  TABLE 1                                                         ______________________________________                                        Reference                                                                              4-nitroaniline/DMSO                                                                           4-chloroaniline/benzene                              ______________________________________                                        NaNH.sub.2                                                                             very dark blue  purplish brown                                       KOH      dark blue       cream                                                NaY-Zeolite                                                                            yellow          cream                                                amorphorous                                                                            faint yellow    cream                                                SiO.sub.2                                                                     ______________________________________                                    

In general terms the catalysts utilized in the instant process comprisea basic, structured, that is a zeolitically structured, alkali(ne-earth)metal-containing aluminosilicate containing in compound form an excessof alkali(ne-earth) metal over that necessary to provide a fully metalcation-exchanged aluminosilicate. More specifically, the instantcatalysts comprise a zeolite and an alkali(ne-earth) metal compound,particularly an oxidic compound, wherein the sum of the amount of thealkali(ne-earth) metal in the compound plus any metal cation exchangedinto the zeolite is in excess of that required to provide a fully metalcation-exchanged zeolite. The alkali(ne-earth) metal compound will befound deposited on the surface of the zeolite. The instant catalystswill contain at least a portion of their pore volume in micropores inthe range of from about three to about twelve angstroms. The instantcatalysts react as bases when placed in solvents and catalyzebase-catalyzed reactions. In a preferred embodiment for shape selectivecatalysis, the alkali(ne-earth) metal compound is substantially locatedon the internal pore surfaces of the zeolite rather than the externalsurfaces.

The instant catalysts retain at least a portion of a crystalline zeolitestructure. The term "crystalline" is employed herein to designate anordered structure capable of being detected by electrooptical ordiffraction techniques, normally by X-ray diffraction, giving aconsistent crystallographic pattern. Such an ordered structure canpersist even after some of the structural silica or alumina is removedfrom the crystal lattice, as by leaching with acids, or with bases suchas might occur during the impregnation process, or by other physical orchemical methods. Sometimes the ordered structure may become soattenuated by these or other means as to fail to diffract X-rays, but insuch cases other electrooptical methods, such as electron beamdiffraction may be utilized. In other cases the crystallite size maybecome so small that diffraction effects may become so diffuse that theamount of crystalline structure may be difficult to detect or determine.In this latter instance, however, the retention of a large surface areaafter chemical and/or physical processing will indicate the retention ofa certain amount crystalline zeolite structure. Thus these lattermaterials are still structured aluminosilicates as opposed to amorphousaluminosilicates and are within the scope of the instant invention.

The catalysts utilized in the instant process, alone or in combinationwith other catalytic components, may be distributed throughout an inertinorganic diluent which also may serve as a binder. Non-limitingexamples of such diluents include aluminas, silicas, silica-aluminas,charcoal, pumice, magnesia, zirconia, keiselguhr, fullers, earth,silicon carbide, clays and other ceramics. In a preferred use of bindersthe instant zeolitic catalysts are intimately mixed a finely divided,hydrous, refractory oxide of a difficulty reducible metal. The term"hydrous" is used to designate oxides having structural surface hydroxylgroups detectable by infrared analysis. The preferred oxides arealumina, silica, magnesia, beryllia, zirconia, titania, thoria, chromia,and combinations thereof such silica-alumina, silica-magnesia, and thelike. Naturally occurring clays comprising silica and alumina may alsobe utilized, preferably after acid treatment. The metal oxide can becombined with the instant catalysts as a hydrous sol or gel, an ananhydrous activated gel, a spray dried powder or a calcined powder. Inone modification a sol or solution of the metal oxide precursor such asan alkali(ne-earth) metal silicate or aluminate can be precipitated toform a gel in the presence of the catalysts utilized in the instantprocess. When less hydrous forms of the metal oxide are combined withthe instant catalysts, essentially any method of effecting intimateadmixture of the components may by utilized. One such method ismechanical admixture, e.g , mulling, which involves admixing the instantcatalysts in the form of a powder with the slightly hydrous, finelydivided form of the metal oxide. The diluent or binder may be added tothe instant catalysts at any point in their preparation, that is,before, during or after impregnation, drying and/or calcination.

The instant catalysts may also be further activated by the incorporationinto the zeolite of additional alkali metal compounds or salts, followedby calcination. For example a catalyst utilized in the instant processmay be impregnated by an aqueous solution of an alkali metal hydroxideor carbonate, dried and calcined to provide an enhanced basic catalyst.

The ranges and limitations provided in the instant specification andclaims are those which are believed to particularly point out anddistinctly claim the instant invention. It is, however, understood thatother ranges and limitations that perform substantially the samefunction in substantially the same way to obtain the same orsubstantially the same result are intended to be within the scope of theinstant invention as defined by the instant specification and claims.

The following illustrative embodiments are provided for illustration andare not to be construed as limiting the invention.

ILLUSTRATIVE EMBODIMENT I. Cracking Catalyst Preparation

The following zeolites were used to prepare the cracking catalysts ofthe instant invention:

1. LZ-Y52 is a zeolite Y molecular sieve obtained from Union CarbideCorporation. It has a unit cell size of about 24.7. a silica to aluminamolar ratio of about 4.7 and a sodium oxide content of about 13 wt. %.

2. USY is a ultrastable zeolite Y that has been dealuminated by acombination of ammonium ion exchange and steaming. It has a unit cellsize of about 24.5, a silica to alumina molar ratio of about 6.8 and asodium oxide content of about 2.5 wt. %.

3. SDUSY is a super dealuminated ultrastable zeolite Y that has beendealuminated by a combination of ammonium ion exchange, steaming andacid leaching. It has a unit cell size of about 24.2, a silica toalumina molar ratio of about 80 and a sodium oxide content of about<0.04 wt. %.

4. 13X is the sodium form of zeolite X molecular sieve obtained fromUnion Carbide Corporation. It has a unit cell size of about 25.0, asilica to alumina molar ratio of about 1.23 and a sodium oxide contentof about 15 wt. %.

Utilizing the above described zeolite substrates, cracking catalystsused in the instant process were prepared as follows:

Preparation of Magnesium Oxide/13X

A 70.9 gram portion of 13X zeolite was washed with deionized water andvacuum dried. The zeolite was then treated with 28 milliliters of anaqueous solution of magnesium nitrate hexahydrate (15.39 grams, 0.0600moles) and vacuum dried. The catalyst was then washed twice with 250milliliters of IN potassium hydroxide and dried under vacuum overnight.

Preparation of Magnesium Oxide/LZ-Y52

A 50.83 gram portion of LX-Y52 was washed three times with 250 millitersof deionized water and dried under vacuum. The zeolite was then slowlytreated with 15 milliliters of an aqueous solution of magnesium nitratehexahydrate (11.04 grams, 0.04305 moles). The catalyst was then driedunder vacuum for 2 hours at 150° C., treated with 10 milliliters ofwater, and dried for an addition 2 hours. The sample was then washedtwice with 250 milliliters of 1N potassium hydroxide and vacuum driedovernight at 150° C.

Preparation of Magnesium Oxide/USY

A 40 gram sample of USY zeolite was impregnated with 15 milliliters ofan aqueous solution of magnesium nitrate hexahydrate (8.8 grams, 0.034moles) and then dried under vacuum. The catalyst was then washed twicewith 250 milliliters of 1N potassium hydroxide and dried under vacuum at150° C.

Preparation of Magnesium Oxide/SDUSY

After being washed three times with 250 milliliters of deionized waterand vacuum dried, a 60 gram portion of SDUSY was treated with 24milliliters of an aqueous solution of magnesium acetate tetrahydrate(11.1 grams. 0.051 moles). After drying, the catalyst was washed twicewith 250 milliliters of 1N potassium hydroxide and dried under vacuumovernight.

Preparation of Cesium Oxide/13X

A 50 gram portion of washed 13X zeolite was impregnated with 54milliliters of an aqueous solution of cesium oxalate (15.0 grams, 0.0423moles). The catalyst was then dried overnight under vacuum.

Preparation of Cesium Oxide/LZ-Y52

After being washed and dried under vacuum, a 20.23 gram portion ofLZ-Y52 zeolite was impregnated with 20 milliliters of a methanolicsolution of cesium acetate (4.38 grams, 0.0228 moles). The catalyst wasthen dried under vacuum overnight at 150° C.

Preparation of Cesium Oxide/USY

A 50 gram sample of USY was impregnated with 54 milliliters of anaqueous solution of cesium oxalate (15.0 grams, 0.0423 moles). Thecatalyst was then dried under vacuum overnight.

Preparation of Cesium Oxide/SDUSY

A 74 gram sample of USY was impregnated with 80 milliliters of anaqueous solution of cesium oxalate (22.0 grams, 0.0622 moles). Thecatalyst was then dried under vacuum overnight.

Preparation of Calcium Oxide/LZ-Y52

After being washed and dried, 20.23 grams of LZ-Y54 zeolite were treatedwith 15 milliliters of an aqueous solution of calcium nitratetetrahydrate (5.38 grams, 0.0228 moles). The catalyst was then dried inan oven at 400° C. for two hours. After cooling to room temperature, thecatalyst was impregnated with 10 milliliters of 1N potassium hydroxide.After 10 minutes the catalyst was washed twice with 250 milliliters of1N potassium hydroxide and dried overnight under vacuum.

Preparation of Barium Oxide/LZ-Y52

After being washed and dried, 20.23 grams of LZ-Y52 zeolite were treatedwith 20 milliliters of barium nitrate (5.95 grams, 0.0228 moles). Afterdrying, the catalyst was washed twice with 250 milliliters of INpotassium hydroxide and the catalyst was dried under vacuum overnight.

II. Catalytic Cracking Experiments

Catalytic cracking experiments were carried out in a stainless steelflow reactor (34 cm by 1.2 cm internal diameter). The feed was meteredinto the flow reactor by the use of a Beckman model 110B pump. Thenitrogen delivery rates were controlled by the use of regulators and theflow rates were measured with a wet test meter. The reaction productswere first cooled with a water condenser as they exit the reactor andthen were further condensed by the use of two cold traps operating at-75° C. In a typical experiment 20 milliliters of catalyst was loadedover a 10 millimeter bed of silicon carbide in the flow reactor. Asecond 10 millimeter silicon bed was placed on top of the catalyst bedto preheat the feed before it contacted the catalyst.

The catalysts were activated by calcination under a nitrogen purge of 50liters per hour at 575° C. for at least one hour. After calcination thenitrogen flow rate was lowered to 22 liters per hour and the reactor wasallowed to cool to the reaction temperature. Hexadecane feed was thenpumped into the reactor at a rate of 2.5 liters per liter of catalystper hour. The contents of the two traps were mixed and analyzed by GCand GC mass spectrometry. The analytical results are presented in Table2. Conversions and selectivities are in weight percents.

                  TABLE 2                                                         ______________________________________                                        Catalytic Cracking                                                            CATA-   Rxn                                                                   LYST    Temp    Conv    LAO  LIO  BIO  PAR  AROM                              ______________________________________                                        Na/Y    550° C.                                                                        94       6.5 8.6   23.0                                                                              30.0  34.9                             Basic   550° C.                                                                        19      27.7 51.8 <1.0 18.5 <1.0                              MgO/13X                                                                       Basic   550° C.                                                                        36      24.8 49.3 <1.0 23.7 <1.0                              MgO/                                                                          LZ-Y52                                                                        Basic   550° C.                                                                        12      41.7 40.0 <1.0 16.3 <1.0                              MgO/USY                                                                       Basic   550° C.                                                                         5      44.3 38.9 <1.0 14.8 <1.0                              MgO/                                                                          SDUSY                                                                         Basic   550° C.                                                                        18      22.1 49.45                                                                               2.0 25.4 <1.0                              Cs.sub.2 O/13X                                                                Basic   550° C.                                                                        28      21.1 51.2 <1.0 25.7 <1.0                              Cs.sub.2 O/                                                                   LZ-Y52                                                                        Basic   550° C.                                                                         9      38.1 42.5 <1.0 17.4 <1.0                              Cs.sub.2 O/USY                                                                Basic   550° C.                                                                         4      42.2 42.5 <1.0 13.3 <1.0                              Cs.sub.2 O/                                                                   SDUSY                                                                         Basic   550° C.                                                                        36      23.3 48.4  2.0 25.3 <1.0                              CaO/                                                                          LZ-Y52                                                                        Basic   550° C.                                                                         6      39.9 47.5 <1.0 10.6 <1.0                              BaO/                                                                          LZ-Y52                                                                        ______________________________________                                         Note: No branched alpha olefins were observed in products                     LAO = Linear Alpha Olefins                                                    LIO = Linear Internal Olefins                                                 BIO = Branched Internal Olefins                                               PAR = Paraffins  excluding hexadecane feed                                    AROM = Aromatics                                                         

What is claimed is:
 1. A process for the catalytic cracking of paraffinswhich comprises contacting at a temperature ranging from about 350° C.to about 650° C. said paraffins with a cracking catalyst comprising azeolite and an alkali(ne-earth) metal compound which has not beencation-exchanged into the zeolite.
 2. The process of claim 1 wherein inthe cracking catalyst, said alkali (ne earth) metal compound is presentin an amount whereby the alkali (ne-earth) metal is in excess of about0.05 times the amount required to provide a fully metal cation-exchangezeolite.
 3. The process of claim 2 wherein in the cracking catalyst, thealkali (ne earth) metal is in excess of about 0.1 times the amountrequired to provide a fully metal cation exchanged zeolite.
 4. Theprocess of claim 3 wherein in the cracking catalyst the alkali(ne earth)metal is in excess of about 0.2 time the amount required to provide afully metal cation-exchanged zeolite.
 5. The process of claim 4 whereinin the cracking catalyst the alkali(ne earth) metal is in excess ofabout 0.5 time the amount required to provide a fully metalcation-exchanged zeolite.
 6. The process of claim 5 wherein in thecracking catalyst, the alkali(ne earth) metal is in excess of about 1times the amount required to provide a fully metal cation-exchangedzeolite.
 7. The process of claim 1 wherein in the cracking catalyst, thealkali(ne earth) compound is an oxidic metal compound.
 8. The process ofclaim 1 wherein the paraffins have carbon numbers ranging from 4 toabout
 35. 9. The process of claim 8 wherein the paraffins have carbonnumber ranging from 4 to about
 20. 10. The process of claim 1 whereinthe zeolite is zeolite X or zeolite Y.
 11. A process for the catalyticcracking of paraffins which comprises contacting at a temperatureranging from about 350° C. to about 650° C. said paraffins with acracking catalyst comprising a zeolite which has been impregnated withan alkali(ne earth) metal compound which has not been exchanged into thezeolite, and calcined at a temperature ranging from about 15° C. toabout 850° C.
 12. The process of claim 11 wherein the cracking catalysthas been calcined at a temperature ranging from about 220° C. to about750° C.
 13. The process of claim 11 wherein the cracking catalyst hasbeen calcined in a nitrogen- or oxygen-containing atmosphere.
 14. Theprocess of claim 11 wherein the paraffins have carbon numbers rangingfrom 4 to about
 35. 15. The process of claim 14 wherein the paraffinshave carbon numbers ranging from 4 to about
 20. 16. The process of claim11 wherein the zeolite is zeolite X or zeolite Y.